1. Field of the Invention
The present invention relates to a semiconductor device (hereinafter referred to as a MEMS component) using a technology of micro electro mechanical systems (MEMS).
2. Description of the Related Art
A MEMS technology is a technology for applying a semiconductor working technique to minutely make up a movable three-dimensional structure (actuator).
According to the MEMS technology, there is a possibility that a small-sized and high-performance component can be developed which is incomparable to existing components. For example, when fusion of an LSI and an individual component is realized, it is not a dream to remarkably reduce a mounting dimension and largely reduce power consumption.
At present, as MEMS components, mainly, a variable capacity, a switch, an acceleration sensor, a pressure sensor, a radio frequency (RF) filter, a gyroscope, a mirror device and the like have been researched and developed (see, e.g., U.S. Pat. Nos. 6,355,498; 6,359,374; and Jpn. Pat. Appln. KOKAI Publication No. 2003-117897).
However, to put these components into practical use, many problems remain to be solved from aspects of performance and manufacturing cost.
In the aspect of the performance, for example, a movable range of an actuator raises a problem. When the actuator comprises a piezoelectric element, and the actuator is movable only by a piezoelectric force, a problem occurs that the movable range is narrowed. On the other hand, to sufficiently secure the movable range, a high voltage must be applied to the piezoelectric element, and it is difficult to lower a voltage.
In the aspect of manufacturing cost, development of a process technology is a keyword, which is capable of realizing high reliability and yield, while reducing the number of steps. However, a cavity has to be formed in a movable section in which an actuator is formed in the MEMS component.
Therefore, a stepped portion causing a residue is easily generated on a semiconductor substrate. Furthermore, a depth of a contact hole with respect to an electrode of a bottom part of the cavity easily becomes excessively large as compared with a depth of another contact hole.
As a result, processes are required: a chemical mechanical polishing (CMP) process for eliminating the stepped portion; a plurality of photo engraving processes (PEP) and the like. These processes complicate and increase steps, and an increase of the manufacturing cost is caused.
Moreover, when the CMP process is adopted, a problem of dishing has to be considered that a polished material surface has a dish form.